Switch to V3 brach of Math.NET Numerics

Despite being in alpha stage I suggest to switch to the V3 branch of Math.NET Numerics already. The major version alpha stage indicates that further breaking changes are expected, but upgrading to final V3 will be much more straightforward from a V3-alpha than from V2.

NB: I can help maintaining this dependency and make sure it integrates nicely (by fixing Math.NET if necessary).